While operating on a workpiece using a conventional metal-cutting machine, such as a milling machine, where the workpiece is clamped to a work table, a dial indicator is periodically mounted in the chuck to gage its various surfaces. The operator must then maneuver the work table to move the workpiece into various desired positions with respect to his work station and to the milling machine axis. The quality or accuracy of the finished product depends on the accuracy with which the dial indicator is used to position the workpiece with respect to the machine axis.
The desired position of the workpiece is first approximated by the operator without the aid of any inspection device. A dial indicator is then inserted into the chuck and used according to known procedures to precisely adjust the location of the workpiece. An existing feature of the workpiece, such as a pilot hole, a slot or workpiece face, is typically used as a reference when positioning the workpiece. For instance, a workpiece may be centered on the machine axis using a dial indicator to compare sides of an existing hole to one another and the machine axis. The dial indicator may be mounted to a crossbar or one leg of an L-shaped bar to provide a convenient way of swinging the indicator through 360 degrees to compare different faces of the workpiece to one another at various radial distances from the machine axis. Prior art procedures, however, are cumbersome and time-consuming, regardless of whether the machine is a standard, manually-operated milling machine, or an automatic machine, such as a computer numeric control (CNC) machine.
The operator uses one hand to turn the machine tool chuck and the indicator mounted therein. The other hand is used to control movement of the machine table. With practice, both hands can be manipulated simultaneously to position the work table and rotate the chuck. However, during this procedure, when the dial indicator is rotated so that its dial face cannot be seen by the operator, the dial indicator cannot simply be rotated for viewing by the operator. The dial indicator must remain undisturbed in relation to the machining axis while measuring a workpiece. Instead, the operator will generally relinquish control of the work table and use one hand to manipulate a hand-held mirror so he can view the dial face while the other hand rotates the chuck.
When the dial indicator is mounted to a crossbar, which allows large workpieces to be measured, the dial indicator may physically interfere with the chuck when the indicator is positioned near the machine axis. This occurs when a feature such as a small hole is being measured and the indicator must be tilted in order to reach the feature near the axis. To avoid interference, the indicator is typically moved outwardly along the crossbar and tilted even further toward the machine axis so the small hole can be measured. By tilting the indicator, however, the dial face is left at an obscure angle and is for the operator difficult to view.
A clamp adapter is generally required to fasten the dial indicator to the tram bar. Prior art clamp adapters, however, are typically configured to receive only one size of dial indicator mount shaft, so each dial indicator must have its own clamp adapter. This results in increased cost to the operator, and increased time spent changing adapters.
A tram bar is needed which facilitates the use of various sizes of dial indicators, and reduces the number of manual tasks which the operator must perform while aligning and measuring a workpiece on a metal-forming machine. The present invention is drawn toward such an inspection device.